1. Field of the Invention
This invention involves the efficacious treatment of an aqueous stream containing governmentally regulated formic acid and/or formaldehyde.
More particularly, this invention relates to a process for destroying formic acid and/or formaldehyde in an aqueous waste stream by precious metal-catalyzed oxidation.
2. Description of the Related Art
It is believed that the present invention can be practiced, generally, in conjunction with aqueous streams containing formic acid and/or formaldehyde.
Given its potential for broad application, the present invention has been shown to have particular advantageous application in treating the formic acid and formaldehyde-containing waste stream generated in connection with the manufacture of N-phosphonomethyl-glycine.
N-phosphonomethylglycine, which is known in the agricultural chemical industry as glyphosate or glyphosate acid, is a highly effective and commercially important herbicide useful in controlling the growth of germinating seeds, emerging seedlings, maturing and established woody and herbaceous vegetation, and aquatic plants.
Glyphosate and its salts are conveniently applied in an aqueous formulation as a broad-spectrum (i.e. effective on a wide variety of plants), post-emergent herbicide. (i.e. effective on a wide variety of plants), post-emergent herbicide.
Various methods are known in the art for the preparation of N-phosphonomethylglycine and its intermediate composition N-phosphonomethylimino-diacetic acid.
For example, in U.S. Pat. No. 4,724,103 to Gentilcore a process for preparing N-phosphonomethyliminodiacetic acid (glyphosate intermediate) is disclosed. This process involves sequentially reacting an alkali metal salt of iminodiacetic acid with a strong mineral acid to form the strong mineral acid salt of iminodiacetic acid and the alkali metal salt of the strong mineral acid and phosphonomethylating the iminodiacetic acid by reaction with formaldehyde and phosphorous acid to provide a mixture of N-phosphonomethyliminodiacetic acid and an alkali metal salt.
Also involved in the process is a step by which the desired intermediate product is separated from other reaction products leaving a formaldehyde-containing waste solution that is readily treatable in accordance with the process of the present invention when formaldehyde and formic acid are distilled out of the heavy organic waste stream by overhead evaporation.
In U.S. Pat. No. 3,969,398 to Hershman, a process is disclosed for the production of N-phosphonomethylglycine by the oxidation of N-phosphonomethyliminodiacetic acid utilizing a molecular oxygen-containing gas as the oxidant in the presence of a catalyst comprising activated carbon.
Characteristic of glyphosate production, such as in this process, there is often provided a conventional distillation step whereby a formic acid and formaldehyde-containing overhead waste stream is formed when these undesirables are separated from the desired N-phosphonomethylglycine product as by distillation.
The liquid waste stream thus formed is a solution containing significant amounts of formaldehyde and formic acid which are substances that cause toxicological concern and are suspected carcinogens.
Eliminating the formaldehyde and formic acid from this stream in high yields is, thus, desirable.
The present invention provides a technically simple and direct process, whereby substantially all of the formic acid and formaldehyde in an aqueous organic stream and, particularly, in waste streams obtained in connection with the production of N-phosphonomethyliminodiacetic acid (i.e. glyphosate intermediate) and N-phosphonomethylglycine or glyphosate acid are eliminated.
This disproportionately high oxidation/conversion of formaldehyde into formic acid and formic acid, in turn, to carbon dioxide and water occurs surprisingly fast and efficiently in connection with the process of the present invention.